Meeting the usa knights can feel like a trip back in time. The modern-day warriors sport old-fashioned gear to fight enemies. But to join team usa, you have to fight for a spot. And the competition is fierce. Tonight, we're storming the battlefield with a soldier who is a first of her kind. Here's ABC's Alex Perez. Reporter: On this battlefield in Spain, the weapons are real. Men are knights. Instead of cheering from the ramparts, women are competing for the very first time. It's the ax-wielding, bone-crushing part of medieval combat. The usa knights, America's team, fighting for gold at the world championships. We few who kneel in the dust have traveled far for this singular task. May we be great. Or may we be not. Use your strengths and your weaknesses. Individual tactics. What do I do? How do I knock somebody to the ground? Reporter: "Nightline" was granted unprecedented access to the team, following them for five months as they prepared to take on the world. Once you step outside the borders of this country, you are the United States team. Reporter: Leading this army, team captain Andre, his military background infects the team with the courtly values of a bygone era. You are the national team of the United States of America. That's something to be proud of. Reporter: There's 70 asperants. This is your olympics? Yes. Reporter: You get emotional. I cry at every patriotic song. It gets to me. Reporter: Don't mistake her pride for weakness. Amy wears real armor and carries steel weapons designed to kill. These are two of the most preferred weapons when you're out there to do some damage. This will bury itself through your flesh. It stops at the bone. You hear a little -- noise. Reporter: Do you think about someone could get seriously hurt when you're out there? Of course. We do everything we can. All the edges on these weapons have to be at least two millimeters wide. The tips have to be rounded out. There's no sharp edges that can puncture. Reporter: The steel armor can cost up to $10,000 and weigh 80 pounds. But anything can happen in the heat of battle. I've seen individuals with their helmet caved in along with their head. I've seen fingers cut off. Guys take their helmet off and there's no teeth left. Reporter: At the last tournament, Amy suffered a bruised hip and a scary concussion, fighting Lisa, her most experienced rival. Before their rematch, women are fighting together. An exhausting group battle called a melee. It's the best of three, long, burning rounds. Where the winner is the team with the last person standing. It's a big ball of adrenaline and blood lust. Something that most women don't get the chance to experience. It's like chocolate, sex, candy, everything all rolled up into one. Reporter: For Amy, this is just the latest challenge on her own personal odyssey. This is what she looked like seven years ago. I was over 450 pounds. I stopped weighing myself because I couldn't find a scale heavy enough for me. Reporter: Where are you now? How did you get there? I had a gastric bypass seven years ago. I can eat two ounces at a time, which is hard for this sport. I run out of fuel much quicker than any man here. Reporter: But the sport has helped you to continue to lose weight. Yes. When they announced that women were going to possibly be able to fight, I started training two hours a night. Reporter: What has it done for your weight loss? I dropped 40 pounds just by doing this. Reporter: Damian is another unlikely combatant. A Colombian and Harvard grad, Damian suffered a broken back in army training. I was a measure for a year. On pain pills and walking with a cane. It seemed like my life was never going to get back together. Reporter: After lengthy rehab, you would think he would be more cautious. But he's inexpublicibly drawn to the carnage. We have doctors, college students. Guys that work at gas stations. This is truly the United States team. Reporter: Nearly 800 spectators crowd the Illinois state fairground cattle yard to cheer on Damian and the others, broken up into melee teams, as they battle for their spot on the national team. Damian's team, the first swords, marches through the competition. And makes it to the finals. Now, it's us against shocking eagles. Reporter: They face off against a team stacked with the best fighters. Now, it's time for the finals. Our friend, Damian. His team made it. They have the red outfits with the white swords. They're about to head out to the battlefield. This match is on. Reporter: First swords lose round one. And in the second, Damian gets cornered. Big hits in there. I was like, man. And into the back. If I didn't have my armor, all of my bones would be broken. Reporter: His gritty display wins him a spot on the team. Then, Amy faces off against Lisa. Lisa is a technical fighter. Reporter: The same opponent who gave her a concussion. And she struggles to hold off the more experienced fighter. Battered, but not broken, Amy is gracious in defeat. And before calling the winner, a huge surprise. She didn't win in tournament. But I'm making you the captain of the melee team. You will be leading this team in Spain. Congratulations. It was an absolute total shock. I had never been so proud of anything in my life. May we live these next few days like men and women of knightly spirits. Reporter: Emotions still raw a month later, as proud knights take the battlefield in Spain. Amy, Damian, and the usa knights turn away challenge after challenge. Cheered on by a crowd of 10,000, and many more watching on Spanish TV. This journey teaches very well that there are some that are stronger than us. Reporter: And one by one, they capture the trophies. Braver than us. More skilled than us. Reporter: They've all battled through so much to get it. But none will be more worthy than us. Reporter: For "Nightline," I'm Alex Perez, in Springfield, Illinois.

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